For the dispersion of fillers and pigments in liquid media it is common to operate with the aid of dispersants in order to reduce the mechanical shear forces required for effective dispersion of the solids and at the same time to obtain very high degrees of filling.
The dispersants support the disruption of agglomerates, wet and/or cover, as surface-active materials, the surface of the particles to be dispersed, and stabilize the particles against unwanted reagglomeration.
Dispersants have become indispensable for the preparation, for example, of highly concentrated color pastes for the paints and coatings industry, for the preparation of pigment concentrates (masterbatches) for the coloring of articles made of plastic, and for the processing of unsaturated polyester resins (UP resins) which comprise large amounts of calcium carbonate or aluminum hydroxide (ATH) as fillers.
The combination of very high degrees of filling in association with a very low viscosity is of particular interest for the producers and users of these products on primarily economic grounds. In the case of the fillers, these commonly constitute the least expensive formulating component; pigment concentrates are intended by the plastics processor to be used for coloring in very highly concentrated form--that is, as far as possible without additional carrier materials.
Phosphoric esters and their use as dispersants are known and can be found in the prior art. For instance, U.S. Pat. No. 4,720,514 describes phosphoric esters of a range of alkylphenol ethoxylates, which can be used with advantage to formulate aqueous pigment dispersions. Phosphoric esters for similar use are described in EP-A-0,256,427. U.S. Pat. No. 5,130,463 and U.S. Pat. No. 5,151,218 report phosphoric esters based on hydroxy-terminated polyaddition products and polycondensation products, which are used for the preparation of highly filled polyester molding compounds, especially for SMC and BMC formulations (SMC=sheet molding compounds; BMC=bulk molding compounds). Bifunctional phosphoric esters prepared by the Mannich-Moedritzer reaction, and their adsorption characteristics on calcium carbonate, are described in J. Appl. Polym. Sci. 65, 2545 (1997).
The known phosphoric esters, however, have the disadvantage that in general they are not universally applicable since there is in many cases a lack of adequate compatibility between the dispersing additive and binder or between the dispersing additive and the surrounding medium (aqueous or solvent-containing formulations). The chemical composition of the phosphoric esters also has a large part to play: in aqueous formulations it is preferred to use only those phosphoric esters whose molecule carries no additional hydrolyzable functional groups, such as ester or urethane groups. Frequently, high levels of dispersing additives are required in order to suppress the incidence of agglomerates; the degrees of filling which can be achieved are unsatisfactorily low, the stability of the dispersions and thus the permanence of the viscosity is often inadequate, and flocculation and aggregation cannot always be avoided, possibly resulting in visible separation and in flow defects and surface defects.